The King has asked Parliament to allow him to appoint the Princess Royal and Earl of Wessex as Counsellors of State – a role that allows them to act formally in Charles's absence.
Counsellors of State, who can deputise for the monarch if he is overseas on an official trip or ill, include the Duke of Sussex, who lives in California after stepping down as a working royal, and the disgraced Duke of York.
Provisions for the counsellors are made under the Regency Act 1937 and those who can stand in for Charles also include the Queen Consort, and the four most senior adults in the line of succession – Prince of Wales, Harry, Andrew and Princess Beatrice.
On Monday the King delivered a message to the House of Commons confirming he wishes to appoint Princess Anne and Prince Edward to the role.
In his message to MPs, Charles said: "To ensure continued efficiency of public business when I am unavailable, such as while I am undertaking official duties overseas, I can confirm that I would be most content, should Parliament see fit, for the number of people who may be called upon to act as Counsellors of State under the terms of the Regency Acts of 1937 to 1953 to be increased to include my sister and brother, the Princess Royal and the Earl of Wessex and Forfar, both of whom have previously undertaken this role."
Penny Mordaunt, the Leader of the House of Commons, said MPs would be able to consider a response to the King's message on Tuesday.
